1. Field of the Invention
The present invetnion relates to a cell which comprises a negative electrode made of lithium or a lithium alloy, a positive electrode comprising polyaniline and a non-aqueous electrolytic solution comprising a lithium salt, and a method for producing polyaniline powder to be used for the fabrication of said positive electrode.
2. Description of the Related Art
Since polyaniline exhibits electrical conductivity through ion doping, a polyaniline cell uses electrode potential change due to change of an amount of ion doping in a conductor region comprising polyaniline as an active material. The polyaniline cell can be used as a secondary cell.
Polyaniline can be synthesized mainly by two polymerization methods, one of which is electrolytic oxidative polymerization comprising electrochemical oxidative polymerization of aniline monomer and the other of which is chemical oxidative polymerization. As the positive electrode material of the polyaniline cell, polyaniline a primary particles of which are of fibrous shape and which is synthesized by the electrolytic oxidative polymerization is preferable in view of cell performance such as capacity.
The polyaniline having the fibrous primary particle shape is prepared by controlling polymerization conditions such as temperature, voltage, current or monomer concentration so that the primary particles become fibrous when a voltage is applied between a pair of electrodes which are dipped in an acidic aqueous solution of aniline or its derivative to deposit polyaniline on one of the electrodes (cf. for example, Preprint for the 24th Cell Forum (1983) 197). Since the polyaniline having the fibrous primary particle shape has good electrical conductivity among the particles due to their shape, the cell comprising the positive electrode made of such polyaniline advantageously has small polarization and a large capacity.
In connection with the chemical oxidative polymerization, various proposals have been made to provide polyaniline which is suitable as the positive electrode material of the cell (cf. Japanese Patent Kokai Publication Nos. 200669/1986, 81420/1987 and 181334/1987).
In the cell comprising the positive electrode made of the polyaniline which has the fibrous primary particle shape and is synthesized by the electrolytic oxidative polymerization, since the polyaniline is crosslinked, crosslinked sites do not contribute to the doping reaction so that a utilization factor of the positive electrode is decreased, discharge life is shortened, and an energy density and load characteristics are insufficient.
The cell having the positive electrode which is made of polyaniline synthesized by the chemical oxidative polymerization does not have satisfactory properties such as discharge life, energy density, load characteristics and the like.